There most certain IS an economy in GTA Online. Have none of you gone to college and studied accounting and/or business law?
All players receive income and have expenses, that defines an economy. Just because there currently isn't a way to interact with other players in respect to financial transactions doesn't mean an economy is non-existent. Player to player transactions would make for a potentially more dynamic economy but due to the hackers C* has rendered that ability, which does exist, to not function.
1. thrifty management; frugality in the expenditure or consumption of money, materials, etc.
As a player who has been gifted Job Shared Money twice in excess of $100,000,000+ each time, my ability to manage my expenses has been, for the time being, rendered moot. I've been able to afford ANYTHING and just as a safe guard for tomorrow 1.08 Patch and Update, I now have 2 garages of fully modded Adders @ $735,550 value each just in case of a most likely cash or bank account wipe, so hopefully my financial future is still secure even if all the cash I have taken away.
Please don't express uninformed opinions about a simple thing as an in-game economy, that is, unless you've never earned any cash nor spent any while playing GTA Online. FFS!